Modern integrated circuits generally contain several layers of interconnect structures fabricated above a substrate. The substrate may have active devices and/or conductors that are connected by the interconnect structure.
Interconnect structures, typically comprising trenches and vias, are usually fabricated in, or on, an interlayer dielectric (ILD). It is generally accepted that, the dielectric material in each ILD should have a low dielectric constant (k) to obtain low capacitance between conductors. Decreasing this capacitance between conductors, by using a low dielectric constant (k), results in several advantages. For instance, it provides reduced RC delay, reduced power dissipation, and reduced cross-talk between the metal lines.
To obtain the desired low dielectric constant, porosity is often introduced into the dielectric material. When vias and trenches are etched in the porous dielectric material, pores are often exposed on the surfaces of the dielectric. These exposed pores typically increase problems that exist when further processing is done on dielectric materials. For example copper formed in the trenches and vias, without a barrier, may diffuse into the dielectric material causing the shorting of adjacent copper lines or line-to-line leakage.
Prior art interconnect structures employ a barrier layer over the surface of the dielectric to protect from copper diffusing into the dielectric material. Yet, any discontinuity in the barrier film will result in the diffusion of copper atoms or penetration of plating solution into the dielectric, which may cause copper lines to short, leakage from line-to-line to occur, and/or destruction of the dielectric material. A thicker barrier layer, which may cover any discontinuities, takes up additional volume in a via or a trench increasing the resistance by reducing the volume available for copper and adding a series resistance to an underlying copper connection.
Therefore, as seen in FIG. 1, related art requires sealing dielectric 120 before a metal conductive layer such as a barrier layer or a copper layer may be formed. As seen in FIG. 1, when sealant layer 125 is formed, conductor 110 has a portion that is exposed to the sealant treatment. Typically, when a portion of conductor 110 is exposed to a sealant treatment, undesirable increases in line resistances, formation of mobile copper ions that increase leakage currents, and electromigration failures may occur.
Related art attempts to protect the copper from sealing by either using mild pore sealing treatments that do not attack the portion of exposed copper or attempting to seal the pores when the copper is not exposed. However, mild pore sealing treatments have been shown to be ineffective, and sealing the pores when copper is not exposed would require etch processing after the treatment, which could degrade the seals.